The answer to your questions is that there is no answer to your question. As a rabbi, I have married couples who became engaged within months of first meeting one another, and also couples who dated, exclusively, for four years before the huppah. Both are normative; both are defensible within Jewish law and broad Jewish custom.

The only part of this to which formal Jewish law would attach itself would be the status of physical intimacy shared by the partners before entering into kiddushin, Jewish marriage. On that topic there are, no surprise, a variety of opinions. Some sources suggest that physical intimacy, and specifically intercourse, itself effects kiddushin, such that couples who are living with one another and sharing such intimacy essentially have the imprimatur of being married. And on the other end of the spectrum, certainly within the ultra-Orthodox community, the very reason for young and short engagements is that no physical contact is permitted before the wedding ceremony; marrying young and quickly thus reduces the chance of going astray by libidinous urges.

In the modern community (and for the purposes of this discussion, I am including all the modern Jewish movements: Reform, Conservative, Modern Orthodoxy [yes—that is a modern Jewish movement! A more-Conservative response to the Conservative Movement’s response to Reform in the 1800s], Reconstructionist, etc…), the normal pattern for how long one waits before getting engaged is the absence of pattern. What Jewish law and custom both encourage is that couplehood be taken seriously, that physical intimacy (however one understands the laws regarding premarital sex) should be expressed and enjoyed in monogamous relationships of mutual respect and safety, and that the decision to get engaged and become married is itself a holy one, one that invokes God into the relationship in an enduring way.

When considering the obligation a Jew has towards tzedakah (and it is an obligation, beyond a suggestion), one must consider both quantity and quality. When it comes to quantity, most sources, building upon the Biblical models, agree that tithing is the goal, or perhaps even the minimum. The major contribution that our ancestors gave to support the "non-profits" of their time was called מעשר/ma'aser, from the Hebrew root meaning "10." They gave a tenth of their income/produce so that the Jewish institutions of that era could be supported. Granted, it is unclear how much civic tax our ancestors were obligated to give beyond that tenth; in our lives, we are enjoined to give tzedakah in addition to our civic tax load. Nonetheless, using one tenth of one's income as a benchmark is a proper way to enter the conversation of quantity.

When it comes to quality, the dominant idea (though by far not the only idea that animates this discussion) for hundreds of years has been the one articulated by Maimonides, the Rambam, who lived from 1134 to 1204. A physician, scientist, philosopher and general savant, Maimonides was chiefly a commentator on Jewish texts and an expert and comprehesive legalist. His code of Jewish law remains a standard that Jews turn to for basic "how to" information on Jewish practice. His famous contribution to the conversation about tzedakah noted 8 distinct levels of giving. The lowest level (which yet still fullfills the basic obligation) is to give unwillingly, in a besmirching manner. As the levels get higher, Maimonides takes into account the experience of the recipient of the tzedakah and the desire to preserve his/her dignity; the value in giving without having to be asked or begged; the value of anonymity in giving; and ultimately, the clear goal of any tzedakah, which is to build the self-sufficiency that will obviate the recipient from needing to rely on tzedakah in the future. Therefore, the highest level according to Maimonides is to give a person a loan, enter into a business partnership with him/her, or help him/her find employment "to strengthen his hand so that he no longer need to be dependent on others." That is the kind of giving to which Jews should aspire. Since such situations do not always present themselves, aspiring to the penultimate level of giving doubly blind, where neither the recipient knows the benefactor, nor the benefactor knows the recipient, is an extraordinary act of goodness itself. Breaking it down more simply: give enough, with a smile, and so that those who received may one day be able to give themselves.

THE VIEWS EXPRESSED IN ANSWERS PROVIDED HEREIN ARE THOSE OF THE INDIVIDUAL JVO PANEL MEMBERS, AND DO NOT
NECESSARILY REFLECT OR REPRESENT THE VIEWS OF THE ORTHODOX, CONSERVATIVE OR REFORM MOVEMENTS, RESPECTIVELY.